Disease steps in multiple sclerosis: a longitudinal study comparing Disease Steps and EDSS to evaluate disease progression

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Abstract
Clinical assessment of outcome in Multiple Sclerosis (MS) patients is problematic since the disease can affect different aspects of the central nervous system and follow a variable course. Recently, we developed Disease Steps, a simple approach for evaluating disease progression. Previously, we found that Disease Steps was easy to use, had uniformly distributed scores and low inter-rater variability. Our current objective was to test the long-term use of Disease Steps together with the most widely utilized clinical outcome measure in MS, the Expanded Disability Status Scale (EDSS) in assessing clinical progression. Over 4 years, 804 patients were classified using both EDSS and Disease Steps. Each patient was assessed at least twice. Follow-up results included annual status and time-to-event analysis examining median staying times within a level of Disease Steps or EDSS. We found that the two scales behaved similarly and correlated strongly with each other. For both Disease Steps and EDSS, patients with milder levels of disability and relapsing-remitting disease demonstrated a higher likelihood of changing scores over time and shorter median staying times compared to more disabled, chronic progressive patients. These findings have important implications for patient selection in clinical trials and for the design of future measurements of clinical outcome in MS. Furthermore, Disease Steps may serve as a simple, practical tool for the nonspecialty neurologist to follow patients over time and serve as a guide in therapeutic decision making. Our findings further document the general progressive nature of MS when a large cohort is followed in an MS specialty clinic over time.